The present invention relates to an electronic endoscope system that is adapted to observe a fluorescence image of autofluorescence emitted from a body cavity wall irradiated with excitation light, as well as a normal image of the body cavity wall illuminated with white light, on a display device such as a monitor.
An example of such an electronic endoscope system is disclosed in Japanese Patent Provisional Publications No. HEI 9-066023. The system disclosed in this publication includes a first solid-state imaging device that takes a fluorescence image, and a second solid-state imaging device that takes an RGB color image with illuminating light in accordance with a frame sequential method. In the system, signals outputted from the first and second solid-state imaging devices are processed by video circuits for fluorescence images and for normal images, respectively. The signals are then synthesized by an image synthetic circuit, and are displayed on a monitor device. According to the operation of a display image selector switch, one of the two kinds of images or both is displayed on the monitor device.
Another example is disclosed in Japanese Patent Provisional Publication No. P2003-33324A. FIG. 11 of the present application shows a block diagram of the system that is illustrated in FIG. 16 of Japanese Patent Provisional Publication No. P2003-33324A. The system disclosed in Japanese Patent Provisional Publication No. P2003-33324A includes (see FIG. 11) a first lamp 124 that emits illuminating light for normal observation and a second lamp 125 that emits excitation light, and either one of the two kinds of light is selectively introduced into a light guide 133 by changing the position of a movable mirror 128. Image signals captured by CCD 137 are stored in a first memory 141 and a second memory 142, and are then displayed on a Hi-Vision monitor 115 through a display location selector circuit 144. When a selector switch for displaying two images (hereinafter, referred to as a two-image-display switch) is turned ON, a normal image and a fluorescence image are displayed on the Hi-Vision monitor 115, simultaneously.
However, when the normal image and the fluorescence image are concurrently displayed as moving images, the brightness of the fluorescence image is dramatically low in comparison with the normal image. Therefore, when both kinds of images are displayed side by side on the monitor as the images are without modification, the great amount brightness difference causes a problem that an observer gets needlessly tired.